Process for the dissolution of cellulose in organic solvents, solutions obtained by said process, and process for the production of formed bodies of regenerated cellulose from said solutions

Abstract

A process for the dissolution of cellulose in organic solvents such as dihylformamide, dimethylacetamide, and N-methylpyrrolidone is described which comprises contacting the cellulose with an excess of paraformaldehyde and with the solvent at elevated temperatures, preferably higher than 115° C. The amount of paraformaldehyde used preferably corresponds to at least 13 CH 2 O units per anhydroglucosidic unit of the cellulose. The solution obtained can be rendered stable at room temperature by heating it under stirring to lower the paraformaldehyde content, preferably to not less than 8 CH 2 O units per anhydroglucosidic unit. Formed bodies of regenerated cellulose can be obtained from said solutions by coagulating them in an aqueous bath, which may be alkaline or may be a mixture of water and the solvent of the solution, or even by evaporating the solvent.

We claim: 
     
       1. A process for the dissolution of cellulose in a solvent selected from the group consisting of dimethylformamide, dimethylacetamide and N-methylpyrrolidone characterized in that the cellulose is contacted with an excess of paraformaldehyde and with said solvent at elevated temperatures. 
     
     
       2. A process according to claim 1, characterized in that the amount of paraformaldehyde used corresponds to at least 13 CH 2  O units per anydroglucosidic unit of the cellulose. 
     
     
       3. A process according to claim 1, characterized in that the temperature is higher than 115° C. 
     
     
       4. A process according to claim 1, characterized in that the cellulose and paraformaldehyde powder are suspended in the solvent and the suspension is heated in a closed vessel under efficient stirring. 
     
     
       5. A process according to claim 1, characterized in that the solution obtained is treated to lower its formaldehyde content. 
     
     
       6. A process according to claim 5, characterized in that the treatment to lower the formaldehyde content is discontinued before the amount of paraformaldehyde in the solution has decreased below 3 CH 2  O units per anhydroglucosidic unit of the cellulose. 
     
     
       7. A process according to claim 5, characterized in that the formaldehyde of the solution is reduced by venting the solution at elevated temperature. 
     
     
       8. A process according to claim 5, characterized in that the formaldehyde of the solution is reduced by producing, in a space communicating with the reaction space, a zone having a temperature lower than the reaction temperature, whereby to cause the condensation of the paraformaldehyde. 
     
     
       9. A process according to claim 8, characterized in that the lower temperature zone is produced by circulation of a cooling fluid. 
     
     
       10. A process according to claim 1 in which the solution is treated to lower the formaldehyde content by cooling the solution to form an opaque solution, and the resulting opaque solution is heated once more under stirring to temperatures close to the temperatures at which it has been formed. 
     
     
       11. A process according to claim 1, characterized in that dimethylsulphoxide is added to the solvent. 
     
     
       12. A process according to claim 1, characterized in that starting products are employed having a low moisture content. 
     
     
       13. A process according to claim 12 characterized in that the moisture content of the starting products is such as to determine a water content of the solution not higher than 0.5%. 
     
     
       14. A process according to claim 12, characterized in that the starting products are dried to reduce the water content to the desired value. 
     
     
       15. Solutions of cellulose derivatives in a solvent selected from the group consisting of dimethylformamide, dimethylacetamide and N-methylpyrrolidione, and containing paraformaldehyde in excess of the anhydroglucosidic units in said cellulose. 
     
     
       16. Solutions according to claim 15, additionally containing dimethylsulphoxide. 
     
     
       17. Solutions according to claim 16, wherein the amount of paraformaldehyde is at least 8 CH 2  O units per anhydroglucosidic unit of the cellulose.